Strong single-tone or multi-tone interference degrades the performance of communication receivers. Such interference may be single-tone or multi-tone signals existing in the transmitting space, or harmonics imported from the circuit board, or residual signal of radio frequency (hereinafter, “RF”) modulation or demodulation, and so on. For single carrier systems, a single-tone or multi-tone interference degrades the effective signal-to-noise (hereinafter, “SNR”). For multi-carrier systems, such as orthogonal frequency division multiplexing (hereinafter, “OFDM”) systems, a single-tone or multi-tone interference not only can destroy data of one or more sub-carriers, but also can decrease the precision of the synchronization and channel estimation. One conventional method for canceling interference detects the frequency of an interference signal and then removes it from the received signal using one or more notch filters. But in practice, a notch filter can not be made ideal and its transition zone may impact data of adjacent sub-carriers, leading to performance degradation of the system.
Conventionally, the frequency of an interference signal in white noise can be detected either in frequency domain or in time domain. For the frequency domain method, the frequency of the interference signal can be detected and estimated by transforming the received signal from time domain to frequency domain using a time-frequency transform such as Discrete Fourier Transform (hereinafter, “DFT”) or Discrete Cosine Transform (hereinafter, “DCT”). But for both DFT and DCT, if the point number is small, estimation precision can be low, and if the point number is large, computing complexity of the transform will be high. Additionally, even if the point number is large, the frequency resolution of the transform is still limited, that is to say the estimated frequency may still deviate from the real frequency of the interference signal. Some advanced signal processing technologies, such as wavelet basis or other basis, may solve the precision problem. However, such technologies are impractical in receivers due to high computing complexity.
For the time domain method, the received signal can be processed through difference processing to generate a sequence having a common phase. The frequency of the interference signal can then be obtained by extracting the common phase from the sequence. In this method, when the SNR is high enough, good performance can be achieved using only a short sequence. But its computing complexity is still very high due to matrix operation though some iterative methods can be used. Further, this method can not track the change of the interference well.
Therefore, it is necessary to provide a method and a system for canceling single-tone or multi-tone interference signals that can solve the above mentioned problems.